Preparation of malonates



Patented Feb. 13, 1 951 PREPARATION OF MALONATES Willard J. Croxall, Bryn Athyn, and John 0. Van Hook, Philadelphia, Pa., assignors to'R-ohm' &' r Haas Company, Philadelphia, Pa, 2; corporation of Delaware No Drawing.

1 This invention relates to the preparation of C-substituted malonates in which the C-substituent is olefinically unsaturated in the betagamma-position thereof. The method of preparation comprising formi'ng an allylically unsaturated ether maleate, rearranging it by heating, and decarbonylating it by heating at 150 to 250 C, For the preparation of the ether maleate the most convenient method includes transetherification of a lower dialkoxysuccinate or alkoxymaleate with an allylicaily unsaturated alcohol in the presence of an alkaline earth metal alcoholat'e.

This application is a continuation-in-part of our. application Serial No. 52,601, filed October 2, 1948;, wherein it was shown that, when an alpha,alpha-di(alkoxy) succinate is heated with an alcohol in the presence of an alkaline catalyst, it, is transetherified and. transesterified. An. alpha-alkoxymaleate acts similarly. During the reaction diether succinate may be dealcoholatedto ethermaleate. In our prior application we pointed out that, when beta-gamma-unsaturated. alcohols are used as reactants, the. transetherification is followed or accompanied by dealcoholaticn of the diether succinate to ether maleate. We now find that, when the transetherification step and dealcoholation are accomplished in the presence of an a'kaline earth metal alcoholate, the ether maleate having an allylic ether substituent may then be transformed and then decarbonylateol to yield an allylmalonate.

The invention can readily be understood through consideration of the chem'cal reactions involved, as will now be illustrated with use of general formulas and equations:

n mooolm HO 02R."

+ (2+n) ROH longer taken up by the mixture, the catalyst is destroyed. as by neutralization with acid or 'by Application March 31-, 1949, Serial No. 84,757

5 Claims. (01. zoo-485) n represents an integer from one to two,R

represents an allylicallyunsaturated residue of a monohydric alcohol, and (R represents the allylic group rearranged. MORI is an alkaline earth metal alcoholate.

The allylically unsaturated alcohol R OH may' be designated with greater detail as R'CII=CHCH2OH wherein R representshydrogen or a lower alkylgroup from methyl tobutyl. When R is hydrogen, R becomes specifically the allyl group proper,

is changed in the rearrangement. Thus, CH3CH=CHCH2-, thecrotyl residue, appears as CHz= CHCH- v H and R.CH'=CHCH2-- is changed to OHz=CHOH"- The diether succinates and ether maleate's referred to above may be synthesized by several A useful one is through the reaction methods. of acetylene on carbonate esters in the presence of strongly basic alkaline catalyst, as describedin'application Serial No. 52,607, filed by Croxall and Schneider on October 2, 1948, now Patent' No. 2,535,012. As there shown, while the main: products are diether propionates and ether acrylates,v there are also obtained diether succinates and ether maleates.v

Acetylene is run into a mixture containing a:- carbonic acid-monohydric alcohol ester and catalyst: at 20 to 110 C. After acetylene is no washing and the. reaction products are. isolated, usually 7 by distillation. present'i'nvention. the diether succinates and ether maleat'es may be collected in a single fraction.

If" desired, the diether succinates may be converted to ether maleates by heating in the presence of an alkali metal acid su'fate and distillingofia mole of alcohol per mole of succinate. Details of this process are given in application For purposes of the Serial No. 52,608, filed by Croxall and Schneider on October 2, 1948. The use of an oxymaleate sometimes proves advantageous in that one mole of alcohol is disposed of before the transetheriflcation and transformation reactions are attempted.

In the reaction of acetylene and carbonate there is used a strongly basic anhydrous catalyst, such as lithium methylate, sodium ethylate, potassium butoxide, or other alkali metal alcoholate, an alkali metal acetylide, such as po-' tassium acetylide or sodium acetylide, and strongly basic. quaternary ammonium alcoholates, such as tetramethyl ammonium methylate, benzyl trimethyl ammonium methylate, ethylate, p'ropylate, or tert.-butoxide, dibenzyl dimethyl ammonium ethylate, etc.

The esters of carbonic acid used have the formulalROhCO where R is a radical of a nontertiary monohydric alcohol which is free of acidic hydrogen and groups reacting with strong alkali. While this group may be widely varied and be aliphatic, cycloaliphatic, or arylaliphatic, saturated or unsaturated, for purposes of the present invention it is the residue'of an alcohol which boils below the allylically unsaturated alcohol used for transetherification. For practical purposes it is desirable to use the smallest convenient groups as R; i. e., the methyl and ethyl groups. These are available through use of methyl carbonate and ethyl carbonate as reactants with acetylene.

The preparation of a typical diether succinate by the above-described method follows. As apparatus, there was used a five-liter flask equipped with a gas-tight stainless steel stirrer, the blades of which scraped the bottom of the flask. For the preparation of catalyst 225 grams of anhydrous ethyl alcohol was placed therein and sodium in small cubes was gradually added for a total of 30 grams of this metal. The sodium was dissolved and excess alcohol was evaporated under reduced pressure, the sodium ethylate remaining as a dry powder. Thereto was added 2200 grams of anhydrous diethyl carbonate. The flask was then equipped with gas inlet and outlet tubes, a manometer, and a thermometer. It was flushed with nitrogen and heated to about 80 C. Acetylene was passed into the system. This gas was drawn from a commercial cylinder but was scrubbed with water and sulfuric acid and then passed over soda-lime. When the rate of absortion of acetylene became very slow, theflask was cooled and the flow of acetylene was discontinued. Dilute acetic acid was added to the system to destroy the alkaline catalyst. Two layers formed in the flask. The upper, oily layer was separated and fractionally distilled.

-..After a forerun had been taken oil at normal diethoxysuccinate was taken off. Atl14-1l5- C./3-4 mm. diethyl alpha,alpha-diethoxysuccinate Was obtained and on further distillation e2 fraction containing this succinate and diethyl alpha-ethoxymaleate was taken off.

In this same way from dimethyl carbonate there are prepared dimethyl alpha,alpha-dimethoxyweare e dim t l. w ime-Ji .w a l t Yet other diether succinates and ether maleates (CH30)2CCOOOH3 CH2=CHCH2OH H2COOCH l(alkaline catalyst) om=cHcH20no o oo CHzCH=CH2 OHzO o o GEE-2011:0115

+ CHsQH l (alkaline catalyst) CHz=CHCH OCCOOCHgCH=CH2 CHF-CHCH2OH CH0 0 O CH2CH=CH2 The transetherified ether maleate is rearranged under the influence of heat to give HOCCOOOHzCH=OHa CH2=CHCHzUCO0CHzOH=CH2 which is an enol form in equilibrium with a keto form.

When alkali metal catalysts are used, the reactions do not stop at this point but proceed to yield alkyl oxalates and allylacetates. Thus,

when sodium methylate is used, as a typical alkali metal catalyst, reactions continue through to dimethallyl oxalate and methallyl methallylacetate,

CH2=CHCH2OCOCOOCH2CH=CH2 and CH2=CHCH2CH2COOCH2CH=CH2 We have found, however, that when an alkaline earth metal is used as the catalyst, desirably in the form of an alcoholate, the reaction does not develop into the above decompositions. The alloxymaleate may be separated and heated at to 250 C. to cause decarbonylation and yield an allyhnalonate. Thus, to continue the above illustration, there is formed from allyl alcohol and ether succinate or maleate the product Suitable catalysts for accomplishing the above result are magnesium methylate, magnesium ethylate, calcium ethylate, magnesium butoxide, magnesium alloxide, and the like. An amount of 1% to 25% of the weight of the starting ether succinate or maleate is ample to promote the desired chemical changes.

The above reaction is effected by heating together an ether succinate or maleate and an allyl alcohol R'CH=CHCHZOH in the presence of an alkaline earth metal alcoholate, displacing the alcohol ROH, and heating the resulting transetherified pr0duct'at-150'toi 2505C.- After transetherification has .been .ef1,

tilled at low pressure.

fected, the catalyst may be destroyed, for the subsequent transformation and decarbonylation appear to be thermal effects. The allylmalonates formed are generally distillable at low pressures.

Examples of the preparation of esters of allylmalonic acids are given to illustrate the invention. 7

Example 1 A mixture of 103 grams of dimethyl alpha,- alpha-dimethoxysuccinate, 1'74 grams of allyl alcohol, 'andmagnesium alloxide, prepared from grams of magnesium reacted with allyl alcohol, was heated in a flask under a four-foot column. At overhead temperatures of 6469 C. there was taken off 68 grams of methanol. Pressure was then reduced and allyl alcohol was distilled from the mixture, the distillation of this alcohol being completed under reducedpressure. Dilute sulfuric acid solution was then added to destroy the catalyst. The mixture was Washed with water, dried over anhydrous magnesium sulfate, and heated from 100 to 190 C. for twentyminutes. About two liters of carbon monoxide were evolved during this time. The mixture was then subjected to distillation under reduced pressure. At 89 to 120 C./2 mm. there was obtained a product which corresponded in composition to allyl allylmalonate. The residue was then heated to 200 C. for thirty minutes. Carbon monoxide was again evolved. The product was again dis- The two distillates were combined and redistilled. The product thus obtained boiled at 93 C./0.5 mm. It had a refractive index, 12 0 1.4545, a density,

53 of 1.030, a molecular refraction, MR of 59.03, and a saponification. equivalent of 114. The theoretical value for MR is 59.53 and for saponification equivalent 112.

Example 2 A mixture of 1.30 grams of diethyl alpha,- alpha-diethoxysuccinate, 170 grams of allyl alcohol, and 30 grams of magnesium alloxide was heated in a flask under a fractionating column until the theoretical amount of ethanol had been taken off. The reaction mixture was then subjected to distillation under reduced pressure until ally alcohol was no longer readily evolved. The mixture was then heated until the temperature of the batch was 200 C. Carbon monoxide was evolved. The batch was then fractionally distilled. The main fraction was identified as allyl allymalonate, boiling at 93 C./0.5 mm. and having a saponification equivalent of Example 3 A mixture of 100 grams of dimethyl alpha,-

alpha-dimethoxysuccinate, 200 grams of crotyl alcohol, and the alcoholate from five grams of magnesium and crotyl alcohol was heated in a flask under a fractionating column. Methanol was displaced as in Example 1 and free crotyl alcohol was taken off under reduced pressure. The catalyst was destroyed with dilute sulfuric acid. The reaction mixture was washed with water, dried, and heated at 190 to 210 C. for twenty minutes. There was then distilled at 100 to 120 C./1-2 mm. a fraction which corresponded in composition to dicrotyl 1-methyl-2- propenylmalonate. V

In the same way other beta,gamina-unsaturated monohydric alcohols may be used in place of the above alcohols. In each case transether- ,ification and transesteriiication are followed by rearrangement and decarbonylation to yield corresponding malonates. These are useful intermediates for forming barbiturates. One C-allyl group is provided from the above .esters and a second C-substituent is readily introduced by conventional methods.

Example 4 The influence of a more strongly basic catalyst than an alkaline earth metal alcoholate is shown in this example. A mixture of 206 grams of dimethyl alpha,alpha-dimethoxysuccinate and 174 grams of allyl alcohol was heated in a flask equipped with a packed distilling column. A solution of four grams of sodium in allyl alcohol was slowly added while the mixture was heated and methanol was distilled therefrom.

Excess allyl alcohol was then distilled off. The

residue was cooled, neutralized with dilute hydrochloric acid and washed with water. It was dried over dehydrated calcium sulfate and distilled. There was obtained at 5'7-59 C./ 10 mm. a fraction which corresponded in composition to allyl allylacetate. At 64-90 C./1 mm. there was obtained a fraction which corresponded in composition with diallyl oxalate. It was redi stilled at 7071 C./1 mm. It had a refractive index of 1.4455, a density of 1.109, a molecular refraction of 41.34 (theory, 41.51), and a saponification equivalent of 87 (theory,

We claim:

1. A process for preparing malonates of the formula COOCH2CH=GHR' catalyst, removing an alcohol ROH from the re-" action mixture, whereby a transetherified ester is formed, heating said transetherifled ester at to 250 C. whereby it is rearranged and decarbonylated and said malonate is formed.

2. The process of claim 1 wherein the ether ester is diethyl diethoxysuccinate.

3. The process of claim 2 wherein the allylic alcohol is allyl alcohol, CH2=CHCH2OHL 4. The process of claim 1 wherein the ether ester is dimethyl dimethoxysuccinate.

5'. The process of claim 4 wherein the allylic alcohol is allyl alcohol.

WILLARD J. CROXALL. JOHN O. VAN HOOK.

REFERENCES CITED The following references are of record in the file of this patent: 1

UNITED STATES PATENTS Number Name Date 2,251,765 Sorenson Aug. 5, 1941 2,281,394 Sorenson Apr. 28, 1942 2,346,612 Rothrock Apr. 11, 1944 

1. A PROCESS FOR PREPARING MALONATES OF THE FORMULA 